from PIL import Image
img = Image.open('./cave.jpg')
width, height = img.size
new_img = Image.new('RGB', (width//2, height//2))
for i in range(width):
    for j in range(height):
        pixel = img.getpixel((i,j))
        new_img.putpixel((i//2-1, j//2-1), pixel) # 奇数
        # new_img.putpixel((i//2, j//2), pixel) # 偶数
new_img.show() ## evil